a. Field of Invention
This invention relates to an optical proximity sensor with reciprocating means for oscillating the length of the optical path between a light source, a target and a light sensor.
b. Description of the Prior Art
Bifurcated optical fibers are frequently used in sensors to detect a distance to a target. Typically, one sensor bundle comprises two sets of fibers, each set originating from a respective arm, the two sets being joined in a common leg. Light is transmitted from a light source through one arm to the target and the corresponding light reflected from the target is conducted by the other arm to a light sensor. The intensity of the reflected light is indicative of the distance between the end of the common leg to the target. However, a direct measurement of the intensity has proven to be in unreliable parameter because of long and short term variations in the intensity of the light source, and variations in the reflectivity of the target. Numerous schemes have been devised in the past to overcome these problems. However, these schemes proved to be unreliable and/or very expensive to implement.
There is a present need for an optical sensor capable of indicating a distance to a target which yields reliable, consistent and accurate results and is inexpensive to make.